Electronic fuel injection systems are unknown which regulate the quantity of fuel provided to an internal combustion engine so that the system fuel delivery schedule exactly meets the requirements of the particular internal combustion engine. Briefly, engine speed and air density are used by the electronic fuel injection system logic circuit to calculate engine-air flow rates since, for a given engine configuration, air flow is proportional to the product of cylinder air density and engine speed. Cylinder air density is equal to the product of manifold air density and engine volumetric efficiency, the latter of which is determined experimentally for each particular engine configuration. It follows that air flow is proportional to the product of manifold air density, engine speed, and engine volumetric efficiency. Fuel flow, then, can be scheduled as any desired function of air flow, by the parameters used to determine air flow, and engine speed. Manifold absolute pressure (MAP), sometimes referred to as manifold air pressure, and air temperature are used to define density.
A throttle position and rate of change of throttle position sensor is also used in known electronic fuel injection systems to provide information to the system control logic to provide modulation of, by small percentages, the basic fuel delivery schedule.
It is known to those skilled in the art that cylinder air density can be approximated as a function of manifold absolute pressure and throttle position. Thus, in electronic fuel injection systems where engine speed is not readily obtainable or for economy purposes an engine speed detector is not desired, the basic system fuel delivery schedule can be calculated in accordance with manifold absolute pressure, throttle position and temperature.
In order to combine signals related to manifold absolute pressure and throttle position nonlinearly, it has been proposed to provide a voltage signal related to throttle position to the gate of a field effect transistor so that the effective resistance through the field effect transistor drain-source circuit varies in accordance with throttle position. A voltage related to manifold absolute pressure is then impressed across a voltage divider which includes the field effect transistor drain-source circuit so that an output voltage is obtained which can be suitably nonlinearly related to manifold absolute pressure and throttle position by proper choice of the system parameters.